Methods and systems for allocating a cellular communications channel for communication between a cellular terminal and a telephone base station using received signal strength measurements

ABSTRACT

A cellular communications channel is allocated for communication between a cellular terminal and a telephone base station wherein the telephone base station connects a wire telephone network to the cellular terminal within a local region in a cell of a wide area cellular network which uses a plurality of control channels and communications channels within a cellular network spectrum, by controlling the cellular terminal to measure the received signal strengths of the control and communications channels. The cellular terminal is controlled to measure received signal strengths of the control channels. A set of communications channels associated with measured control channel having lowest received signal strength is identified. The cellular terminal is then caused to measure the received signal strengths of the set of communications channels. A communications channel having the lowest received signal strength is selected from the set of communications channels. The selected communications channel having lowest received signal strength is used for communication between the cellular terminal and the telephone base station within the local region. The selected communications channel reduces co-channel interference between the telephone base station and the wide area cellular network and also reduces co-channel interference among the telephone base stations themselves.

FIELD OF THE INVENTION

This invention relates to communications systems and more particularlyto radio personal communications systems for use within wide areacellular networks.

BACKGROUND OF THE INVENTION

Radio communications systems are increasingly being used for wirelessmobile communications. An example of a radio communications system is awide area cellular phone network. Cellular radio communications systemsare wide area communications networks which utilize a frequency(channel) reuse pattern. The design and operation of an analog cellularphone system is described in an article entitled Advanced Mobile PhoneService by Blecher, IEEE Transactions on Vehicular Technology, Vol.VT29, No. 2, May, 1980, pp. 238-244. The analog mobile cellular systemis also referred to as the "AMPS" system.

Recently, digital cellular phone systems have also been proposed andimplemented using a TimeDivision Multiple Access (TDMA) architecture.Standards have also been set by the Electronics Industries Association(EIA) and the Telecommunications Industries Association (TIA) for anAmerican Digital Cellular (ADC) architecture which is a dual mode analogand digital system following EIA/TIA document IS-54B. Telephones whichimplement the IS-54B dual mode architecture are presently being marketedby the assignee of the present invention. Different standards have beenpromulgated for digital cellular phone systems in Europe. The Europeandigital cellular system, also referred to as GSM, also uses a TDMAarchitecture.

Proposals have recently been made to expand the cellular phone networkinto a radio personal communications system. The radio personalcommunications system provides mobile radio voice, digital, video and/ormultimedia communications using radio personal communications terminals.Thus, any form of information may be sent and received. Radio personalcommunications terminals include a radio telephone, such as a cellulartelephone, and may include other components for voice, digital, videoand/or multimedia communications.

A radio personal communications system includes at least one telephonebase station also referred to herein as a base station. A base stationis a low power transceiver which communicates with a radio personalcommunications terminal such as a cellular terminal over a limiteddistance, such as tens of meters, and is also electrically connected tothe conventional public wire network. The base station allows the ownerof a radio personal communications terminal to directly access the wirenetwork without passing through the cellular phone network, whose accessrates are typically more costly. When located outside the range of thebase station, the personal communications terminal automaticallycommunicates with the cellular phone network at the prevailing accessrates.

A major problem in implementing a radio personal communications systemusing a common frequency allocation for both the base station and thecellular phone network is the frequency overlap between the cellularphone network and the base station. As understood by those having skillin the art, only a limited number of frequencies are available for radiocommunications. In the United States, cellular phone networks have beenallocated 832 30 kHz wide channels. Within this spectrum, each regionalprovider can substantially allocate and use these frequencies as it seesfit. Additional ranges of frequencies are also being allocated in theUnited States for use as wide area cellular communications networks.

Cordless phones, such as those used by individuals in their homes,utilize a separate range of frequencies, in the United States from 46MHz to 49 MHz. Therefore, they are able to operate within a cellularnetwork without interference. However, such phones are unable to operateas cellular phones connected to the cellular network when out of rangeof their individual base stations. Dual mode phones which operate bothas a cellular phone within the cellular frequency range (824-894 MHz)and as a conventional cordless phone (46-49 MHz) are described in U.S.Pat. No. 4,989,230 to Gillig et al.

Frequency overlap between the network and the base stations can beprevented if the network and base stations are allocated different bandsof frequencies as with the dual mode cellular and cordless phonediscussed above. However, such a hybrid system is not an efficientallocation of the frequency spectrum. Moreover, a hybrid personalcommunications terminal may be more expensive and complicated becauseadditional circuitry may be required.

A major advance in preventing frequency overlap between the network andthe base stations is described in U.S. Pat. No. 5,428,668 to the presentinventors, entitled Radio Personal Communications System and Method forAllocating Frequencies for Communication Between a Cellular Terminal anda Base Station, assigned to the assignee of the present invention, thedisclosure of which is hereby incorporated herein by reference. In the'668 Patent, a base station connects a wire telephone network to thecellular terminal within a local region of a wide area cellular network.The base station includes a housing, which is preferably portable, and awire telephone network connector extending within the housing forconnecting the base station to the wire telephone network. Activationmeans within the housing is also electrically connected to the wiretelephone network connector for detecting an incoming call on the wiretelephone network. A radio transceiver within the housing is responsiveto the activation means for communicating with the cellular terminalusing a selected frequency within the spectrum of the wide area cellularnetwork when the cellular terminal is within range of the base station.When the cellular terminal is not within the range of the base station,communications take place from the cellular terminal to the wide areacellular network. The communications through the base station occur at aselected frequency (channel) within the spectrum of the wide areacellular network, but at the lower billing rates of the wire telephonenetwork, and can occur without adding to the load on the wide areacellular network.

Same channel interference between the wide area cellular network and thebase station is reduced by selecting an available channel within thecellular spectrum for communications between the cellular terminal andthe base station when the cellular terminal is within range of the basestation. The selected channel utilizes one of the frequencies of thewide area cellular network which is not allocated to the cell of thewide area cellular system in which the base station is located.

As described in the '668 Patent, frequency indicating signal is receivedby the base station or the cellular terminal from the wide area cellularnetwork operator over the wire telephone network, responsive to arequest from the base station or the cellular terminal. This allows thenetwork operator to assign frequencies for base stations which minimizesame channel interference with the wide area cellular network. Thesystem carrier also can obtain additional revenue from unusedfrequencies within a network cell by leasing these frequencies for basestation operation within the cell. The frequency assignment request maybe initiated automatically upon application or reapplication of power tothe base station. Alternatively, manual user intervention may berequired.

In another aspect of the '668 Patent, the base station detects if theelectrical connection of the wire telephone network to the wiretelephone network connector has been lost and prevents the transceiverfrom transmitting at the previously selected frequency if the connectionhas been lost. This prevents a base station from being disconnected andreinstalled in a new location where the previously selected frequencycould interfere with frequencies in use in that area by the wide areacellular network. Optionally, this detection and disable aspect respondsto loss of both the power and telephone connections rather than justloss of the telephone connection or power connection.

Notwithstanding the significant improvement of the allocation system andmethod of the '668 Patent, additional techniques for allocating acellular communications channel between a cellular terminal and atelephone base station may be desirable. For example, the '668 Patentmay require the operator of the wide area cellular network to haveknowledge of the cell within which the telephone base station is locatedin order to be able to identify a cell which is further away. Moreover,the '668 Patent may not solve the problem of mutual interference betweentwo telephone base stations. The wide area cellular network operator mayassign the same channel to two adjacent telephone base stations havingoverlapping local regions and thereby create co-channel interferencebetween the base stations themselves.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide methodsand systems for allocating a cellular communications channel forcommunication between a cellular terminal and a telephone base station.

It is another object of the invention to provide methods and systems forallocating a cellular communications channel for communication between acellular terminal and a telephone base station without requiringknowledge of the location of the telephone base station.

It is yet another object of the present invention to provide methods andsystems for allocating a cellular communications channel forcommunication between a cellular terminal and a telephone base stationwhich reduce co-channel interference between adjacent telephone basestations having overlapping local regions.

These and other objects are provided according to the present inventionby using the cellular terminal to measure received signal strength ofcontrol channels and communications channels (also known as "voicechannels" or "traffic channels") within the local region and using thereceived signal strengths to allocate a cellular communications channelbetween the cellular terminal and the telephone base station. Theselected communications channel reduces co-channel interference betweenthe telephone base station and the wide area cellular network and alsoreduces co-channel interference among the telephone base stationsthemselves.

In particular, according to the invention, a cellular communicationschannel is allocated for communication between a cellular terminal and atelephone base station wherein the telephone base station connects awire telephone network to the cellular terminal within a local region ina cell of a wide area cellular network which uses a plurality of controlchannels and communications channels within a cellular network spectrum.The cellular terminal is controlled to measure received signal strengthsof the control channels. A set of communications channels associatedwith a measured control channel having lowest received signal strengthis identified. The cellular terminal is then caused to measure thereceived signal strengths of the set of communications channels. Acommunications channel having the lowest received signal strength isselected from the set of communications channels. The selectedcommunications channel having lowest received signal strength is usedfor communication between the cellular terminal and the telephone basestation within the local region.

By controlling the cellular terminal to measure received signal strengthof the control channels, the communications channels associated withcells which are farthest away from the base station are used, therebyreducing interference between the telephone base station and the widearea cellular network. Moreover, by causing the cellular terminal tomeasure received signal strengths of the set of communications channelsassociated with the control channel having lowest received signalstrength, interference with other telephone base stations is reduced.Accordingly, interference with the wide area cellular network and withother base stations is reduced without the need for the wide areacellular network operator to know the exact location of the telephonebase station.

The communications channel having lowest received signal strength maystill not be sufficiently low to prevent interference with adjacent basestations. If this is so, the set of communications channels associatedwith the measured control channel having the next lowest received signalstrength is identified and the cellular terminal measures the receivedsignal strengths of this next set of communications channels. Thecommunication channel having the lowest received signal strength fromthe next set of communications channels is then selected and used forcommunications. These operations may be repeated until a communicationschannel having acceptably low signal strength is identified.

The cellular terminal may itself compare the received signal strengthsin order to identify the measured control channel having lowest receivedsignal strength and the measured communications channel having lowestreceived signal strength. Alternatively, the received signal strengthsmay be relayed to the telephone base station, which compares thereceived signal strengths and identifies the lowest measured receivedsignal strength from the list provided by the cellular terminal.However, most preferably, the wide area cellular network obtains thereceived signal strength measurements from the cellular terminal via thebase station and wire telephone network, and determines the channelhaving the lowest received signal strength. Accordingly, in identifyinga set of communications channels associated with a measured controlchannel having lowest received signal strength, the control channelreceived signal strength measurements are preferably transferred fromthe cellular terminal to the telephone base station and from thetelephone base station to the wide area cellular network via the wiretelephone network. The wide area cellular network identifies a measuredcontrol channel having lowest received signal strength and the wide areacellular network identifies the set of communications channelsassociated with the measured control channel having a lowest receivedsignal strength. Similarly, in causing the cellular terminal to measurereceived signal strengths of the set of communications channels, theidentified set of communications channels is preferably transferred tothe base station from the wide area cellular network via the wiretelephone network and then from the base station to the cellularterminal.

Similarly, in selecting a communications channel having lowest receivedsignal strength from the set of communications channels, the receivedsignal strength measurements are preferably transferred from thecellular terminal to the telephone base station and from the telephonebase station to the wide area cellular network via the wire telephonenetwork. The wide area cellular network identifies a measuredcommunication channel having lowest received signal strength and thewide area cellular network selects the communication channel havinglowest received signal strength. The identification of the selectedcommunications channel is then transferred to the base station via thewire telephone network and from the base station to the cellularterminal.

Preferably, the received signal strength is measured by the cellularterminal and measurements and other signals are passed between thecellular terminal and the wire telephone network via the base station,while the cellular terminal is parked in the telephone base station. Thesignals and measurements may be transferred via electrical signals,electromagnetic signals such as optical signals, or acoustic signalssuch as ultrasound signals. Accordingly, the cellular terminal iscontrolled to measure received signal strength of control channels andcommunications channels in the local region so that the wide areacellular network can allocate a channel for communication between thecellular terminal and telephone base station while reducing co-channelinterference with the wide area cellular network and with othertelephone base stations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B schematically illustrate a radio personal communicationssystem including a base station and a cellular terminal, with radiocommunications between the terminal and the base station, and radiocommunications between the terminal and a wide area cellular network,respectively.

FIG. 2 illustrates a front perspective view of an embodiment of a basestation, with a terminal shown in hidden lines.

FIG. 3 is a schematic block diagram of the base station of FIG. 2.

FIG. 4 is a schematic block diagram of the base station transceiver ofFIG. 3.

FIG. 5 is a schematic block diagram of a cellular terminal.

FIG. 6 is a flowchart illustrating operations during initialization of aradio personal communications system according to U.S. Pat. No.5,428,668.

FIG. 7 is a schematic illustration of a first cell re-use pattern for awide area cellular network.

FIG. 8 is a schematic illustration of a second cell re-use pattern for awide area cellular network.

FIG. 9 is a flowchart illustrating operations of a radio personalcommunications system according to U.S. Pat. No. 5,428,668.

FIGS. 10A and 10B are a flowchart illustrating operations of a radiopersonal communications system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

This Detailed Description will begin with a description of radiopersonal communications systems and methods for channel allocationaccording to U.S. Pat. No. 5,428,668. Then, methods and systems forchannel allocation using received signal strength measurements accordingto the present invention will be described.

Radio Personal Communications System

Referring to FIGS. 1A and 1B, conceptual diagrams of a radio personalcommunications system are shown. Such a system operates within a widearea cellular network which allocates portions of a plurality offrequencies (channels) within a cellular network spectrum to separategeographic cells. Thus, the system provides a wide area wirelesscommunications network having the capacity to provide high qualitywireless communications to a large number of users with a limited numberof frequencies allocated to the wide area cellular network. As shown inFIG. 1A, a wide area cellular network includes at least one radionetwork cell station 102, such as a cellular telephone cell station, fortransmitting and receiving messages in a network cell indicated by 104,via cell antenna 106. The cell 104 of radio network cell station 102 istypically represented graphically as illustrated in FIGS. 1A, 1B, 7 and8. Radio network cell station 102 also interfaces with the wiretelephone network 108. It will be understood by those having skill inthe art that a wide area cellular network 100 typically includes manyradio network cell stations 102 to cover a large area as illustrated inFIGS. 7 and 8. In such a system each radio network cell station 102covers a cell 104 within wide area cellular network 100 and mayinterface with a central station (not shown) by wireless (radio)communications. The central station may provide the connection to wiretelephone network 108 for all of the network cell stations 102 that makeup wide area cellular network 100.

Still referring to FIG. 1A, a telephone base station 110 is locatedwithin the cell 104 of a network cell station 102 of wide area cellularnetwork. Base station 110 includes a low power transceiver fortransmitting and receiving via base station antenna 112, over a limitedlocal region 114, typically on the order of tens of meters. Thus, a basestation may be used for transmission and receipt of radio personalcommunications in a home or office. Base station 110 also iselectrically connected to the wire telephone network 108. Wire telephonenetwork 108, is also referred to as the Public Switched TelephoneNetwork (PSTN). PSTN 108 is the regular "wire line" telephone systemsupplied by, for example, the regional Bell Operating Companies, and mayuse copper wire, optical fiber or other stationary transmissionchannels. Base station 110 may be wired directly to PSTN 108 or connectthrough a PABX (not shown).

Still referring to FIG. 1A, a radio personal communications terminal 120is shown for radio communications with both base station 110 and radionetwork cell station 102 via antenna 122. Radio personal communications(cellular) terminal includes a radio telephone such as a cellular phone.Cellular terminal 120 may also include, for example, a full computerkeyboard and display, a scanner, and full graphics and multimediacapabilities.

As illustrated in FIG. 1A, when terminal 120 is in the local region 114of the base station 110, a radio link 124 therebetween is established.As shown in FIG. 1B, when the terminal 120 is outside the local region114 of the base station 110, but within the cell 104 of the network cellstation 102, a new radio link 126 is automatically established with thenetwork cell station 102 to establish communications through wide areacellular network 100. Thus, when the user is relatively close to thebase station 110 (i.e. within the home or office), wirelesscommunications take place with the base station so that wide areacellular network, with its higher billing rate structure, is bypassed.When the user is relatively far from the base station 110,communications take place with the cellular network.

It will be understood by those having skill in the art that a completeradio personal communications system will typically include many basestations 110, terminals 120 and radio network cell stations 102. It willalso be understood by those having skill in the art that conventionalcommunications and handoff protocols may be used with the radio personalcommunications system, and need not be described further herein. Forpurposes of this description, it will be assumed that the spectrumallocation for the radio network cells is the IS-54B cellular phonespectrum allocation which is illustrated in Table 1 below.

                  TABLE 1                                                         ______________________________________                                                                      Transmitter Center                                                   Boundary Frequency                                       Bandwidth   Number of                                                                              Channel  (MHz)                                           System (MHz)    Channels Number MOBILE BASE                                   ______________________________________                                        Not Used        1               (824.010)                                                                            (869.010)                              A*     1        33       991    824.040                                                                              869.040                                                         1023   825.000                                                                              870.000                                A      10       333      1      825.030                                                                              870.030                                                         333    834.990                                                                              879.990                                B      10       333      334    835.020                                                                              880.020                                                         666    844.980                                                                              889.980                                A'     1.5      50       667    845.010                                                                              890.010                                                         716    846.480                                                                              891.480                                B'     1.5      83       717    846.510                                                                              891.510                                                         799    848.970                                                                              893.970                                ______________________________________                                        Transmitter                                                                           Channel Number Center Frequency (MHz)                                 ______________________________________                                        MOBILE  1 ≦ N ≦ 799                                                                    0.030 N + 825.000                                              990 ≦ N ≦ 1023                                                                 0.030 (N-1023) + 825.000                               BASE    1 ≦ N ≦ 799                                                                    0.030 N + 870.000                                              990 ≦ N ≦ 1023                                                                 0.030 (N-1023) + 870.000                               ______________________________________                                    

In the radio personal communications system described in FIGS. 1A and1B, it is important to avoid same channel interference between basestation 110 and the radio network cell station 102. Same channelinterference can be avoided by using two discrete spectra for thenetwork calls and for the base station. For example, the base stationcan use cordless telephone protocols. Unfortunately, this requires theterminal 120 to operate under both cellular and cordless protocols,which may be costly and wasteful.

According to U.S. Pat. No. 5,428,668, the operator of network 100, whichhas typically been assigned the use of a specific plurality offrequencies within a frequency spectrum of a designated geographicregion by a regulatory authority, is allowed to assign frequencies andoptionally power levels, of base station 110. The wide area cellularnetwork operator (provider) can assign frequencies and optionally powerlevels to base station 110 to minimize same channel interference and tomaximize revenue from the assigned frequency spectrum.

Base station 110 uses the obtained frequency and power level,respectively, to govern operation of base station 110. Frequency andpower level signals may also be used to control operation of the radiopersonal communications (cellular) terminal 120 as will be describedbelow. As will also be described below cellular terminal 120 may becontrolled to operate at the same frequency and power level as basestation 110. Alternatively, a different frequency and power level may beprovided. Thus, the wide area cellular network operator can receiverevenue from the use of the frequency, and simultaneously prevent radiocommunications between base station 110 and terminal 120 frominterfering with communications within cellular network 100.

An embodiment of a base station and cellular terminal is illustrated inFIG. 2. Base station 110 includes housing 130 which is adapted tocooperatively mate with cellular terminal 120 and provide an electricalinterface between base station 110 and cellular terminal 120 usingelectrical connector 132 or other electrical connecter means.Alternatively, electromagnetic communications such as opticalcommunications, or acoustic communications such as ultrasoniccommunications, may be provided via an appropriate connector andinterface. Base station 110 is connected to a power source (poweroutlet) by power line connection 134 or other power connection means andto a wire telephone network by a wire telphone network connector 136extending from base station 110 to within housing 130 or other means forelectrically connecting base station 110 to a wire telephone network. Asshown in FIG. 2, housing 130 is preferably portable to allow the user tomove it and reinstall it in different locations. Base station 110 asillustrated in FIG. 2 may further include battery charger connector 138or other charger interface means which connects battery powered cellularterminal 120 to a battery charger (not shown in FIG. 2) when cellularterminal 120 is inserted or parked in housing 130 as illustrated byhidden lines in FIG. 2. Sensor 140 detects when cellular terminal 120 isparked in housing 130 and the battery charger is activated to charge thebattery of battery powered cellular terminal 120. It will be understoodby those having skill in the art that a separate sensor 140 need not beused to detect when terminal 120 is parked in housing 130.

Base station 110 as illustrated in FIG. 2 also includes display 142 orother user inidcating means. Alternatively, cellular terminal 120 mayinclude an indicating means which may be used to display signals frombase station 110 transmitted over electrical connection 132 whencellular terminal 120 is parked in housing 130. Base station 110 mayalso include keyboard 144 or other user input means. Alternatively, aswith display 142, celllular terminal 120 may inlucde an input meanswhich may be used to provide inputs to base station 110 when cellularterminal 120 is parked in housing 130.

A block diagram of an embodiment of a base station 110 is illustrated inFIG. 3. Power supply 150 is connected to power line connector 134 andprovides the power supply voltages to the circuitry of base station 110.Power supply 150 further includes power detection means 151 fordetecting when the connection of power line connector 134 to the powersource has been lost and for providing a sense signal to controlprocessor 154 indicating that power has been lost.

Ringing current and exchange battery voltage detector 152 iselectrically connected to wire telephone connector 136 and includesmeans for detecting an incoming call on wire telephone connector 136which is connected to wire telephone network 108. Detector 152 furtherdetects if the electrical connection of wire telephone network 108 toconnector 136 has been lost. Detector 152 supplies signals to controlprocessor 154 when an incoming call "ring" is detected and when theconnection to wire telephone network 108 is lost. An indication that thewire telephone network (line) connection has been lost may then be sentto display 142 under the control of control processor 154.

Control processor 154, in cooperation with ringing current and exchangebattery voltage detector 152 provide activation means for initiatingcommunications between wire telephone network 108 and cellular terminal120 through base station 110 when cellular terminal 120 is within region114. For incoming calls from wire telephone network (line) 108, detector152 detects the incoming call and sends an activation signal to controlprocessor 154 which in turn controls subsequent communicationsoperations of base station 110. For calls initiated from cellularterminal 120, control processor 154 detects the communication fromcellular terminal 120 received by transceiver circuit 164 or other radiotransceiving means connected to antenna 112 at a selected frequencywithin the spectrum of wide area cellular network 100. Control processor154 sends a control signal to detector circuit 152 to generate OFF-HOOKand other signals such as pulse dialling that may be necessary tointerface with a loop-disconnect line interface such as is typicallyused by wire telephone network 108.

Splitter circuit 156 effects a split of the two-wire, bidirectionaltelephone audio signal into a four-wire system of separate send andreceive signals. Received signals from the wire telephone network 108are converted from analog to digital by analog to digital converter (Ato D) 158 while transmit signals to wire telephone network 108 areconverted from digital to analog by digital to analog converter (D to A)160. This allows all of the subsequent audio signal processing to becarried out digitally using digital signal processors. Echo canceler 162attenuates echoes of the signal sent through connector 136 to PSTN wirenetwork 108 to inhibit corrupting of the signal received from the PSTN.Echo canceler circuit 162 further prevents echoes being transmitted tocellular terminal 120 by transceiver circuit 164 or other radiotransceiving means connected to antenna 112.

On incoming calls over wire telephone network (line) connector 136,transceiver circuit 164 responds to the ring detect from detector 152under the control of processor 154 to communicate with cellular terminal120 using a selected frequency within the frequency spectrum of the widearea cellular network 100. Storage circuit 155 or other storage means iselectrically connected to control processor 154 to provide a storagecapacity for program and data information such as a frequency indicatingsignal representing the selected frequency. Storage circuit 155 mayinclude conventional readable and writable memory such as RAM or EEPROM.

After echo cancellation, modem 166 processes received digitized audiosignals to extract any digital control messages that might be receivedalong with the audio signal from the wire telephone network (line). Suchdigital control messages may, for example be programming information forbase station 110 transmitted by the operator of wide area cellularnetwork 100. Extracted digital control messages are passed to controlprocessor 154. Modem 166 may perform data/speech discrimination. Adigital signal processor such as Texas Instruments type TMS320C56 may beused for echo canceler 162 and modem 166.

Received digitized speech is passed to transceiver 164 for transmission.The digitized speech may first be compressed by compression circuit, notshown, to a lower bit rate using a conventional speech decodingalgorithm such as CELP or VSELP. In an analog transmission embodiment ofbase station 110 of the present invention a conversion circuit, notshown, reconverts the discriminated speech to an analog signal formodulating transceiver 164 which in this embodiment is an analogtransceiver.

Radio signals from cellular terminal 120 to base station 110 received byantenna 112 are detected and converted to digital speech signals bytransceiver 164. The digital speech signals are then passed to echocanceler circuit 162 and modem circuit 166 for transmission on wiretelephone network (line) connector 136 to wire network 108.Alternatively, the received signals may be digitized to complex numberform, using for example the LOGPOLAR technique described in U.S. Pat.No. 5,048,049. The complex number stream is then passed to modem 166 fornumerical demodulation and conversion to analog speech for sending onthe wire telephone line.

The radio personal communications system may also be used for datatransmission from cellular terminal 120 when cellular terminal 120either incorporates a personal computer system or by plugging cellularterminal 120 into a personal computer to connect the computer to modemcircuit 166 without the use of a direct wire telephone line cableconnection to the computer. When handling data transmissions, modemcircuit 166 and transceiver 164 translate the data stream between theover-the-air protocols used and normal wire telephone line datatransmission protocols. Transceiver 164 may also detect when thereceived signal has reverted to voice and, responsive to controlprocessor 154, effect a reversion of modem circuit 166 and echo cancelercircuit 162 to the processing of voice signals.

Transceiver 164 may be selected to generate and receive signalsconforming to any standard, for example, AMPS, ETACS, NMT450, NMT900,GSM, DCS1800 or IS54. In addition, transceiver 164 may generate orreceive signals conforming to air-interface standard for communicationswith satellite systems, such as INMARSAT-M, INMARSAT-P, IRIDIUM,ODYSSEY, GLOBALSTAR, ELLIPSAT or M-SAT. All such standards may beutilized with the present invention to provide communications fromcellular terminal 120 through normal PSTN wire lines 108 and avoidingusing the wide area system.

FIG. 4 illustrates a schematic block diagram of a radio transceiver 164of FIG. 3. As shown, transceiver 164 includes circuitry for both thereception and transmission of the radio frequency signals. Signalsreceived by the antenna 112 are directed to the receive circuits by theduplexer 201. The duplexer is a filter with two separate bandpassresponses: one for passing signals in the receive band and another forpassing signals in the transmit band. Duplexer 201 allows simultaneoustransmission and reception of signals by using different receive andtransmit frequencies. For example, in the AMPS or IS54B architectures,the receive and transmit frequencies are separated by 45 MHz.

After passing through the duplexer 201, received signals are amplifiedby a low noise radio frequency (RF) amplifier 202. This amplifierprovides just enough gain to overcome the expected losses in the frontend circuitry. After amplification, unwanted components of the signalare filtered out by the receive filter 203. After filtering, the signalis mixed down to a first intermediate frequency (IF) by mixing it inmixer 204 with a second signal generated by the channel synthesizer 215and filtered by Local Oscillator (LO) filter 214. The first IF signal isthen amplified by amplifier 205 and unwanted mixing products are removedby IF filter 206. After filtering, the first IF is mixed in mixer 207 toyet another lower frequency or second IF signal, using a signal providedby local oscillator synthesizer 216. The second IF signal is thenfiltered by two filters 208 and 210, and amplified by multistageamplifiers 209 and 211 to obtain an IF signal 212 and a radio signalstrength indication (RSSI) signal 213. Thereafter, it undergoes aprocess of detection, for example, as described in U.S. Pat. No.5,048,059 to Dent, the disclosure of which is incorporated herein byreference.

In order to transmit, a datastream 219 is generated by modem 166 (FIG.3). In ADC architecture, the datastream is organized as bursts for timedivision multiplexing with other users. Reference oscillator 218generates a precise frequency which is used as a stable reference forthe RF circuits. The output of oscillator 218 is passed through amultiplier 221 where it experiences a sixfold increase in frequency.This frequency is then passed into a quadrature network 222 whichproduces two signals of equal amplitude which have a quadrature phaserelationship, i.e. they are offset by 90°. These quadrature signals,along with the datastream 219, are combined in the modulator 223 tocreate a modulated signal, as described in an article entitled I and QModulators for Cellular Communications Systems, D. E. Norton et al.,Microwave Journal, Vol. 34, No. 10, October 1991, pp. 63-79. Themodulated signal is passed to a mixer 224 which translates the signal toradio frequency. The exact radio frequency is determined by the localoscillator signal provided by the channel synthesizer 215. The radiofrequency signal is passed through a variable gain controlled amplifier225. The gain of this amplifier, which is controlled by means of avoltage on transmit power control line 220, determines the eventualoutput power, since the linear power amplifier 227 has fixed gain.Filtering is performed by transmit filter 226.

Referring now to FIG. 5, the design of cellular terminal 120 is similarto that of base station 110 (FIG. 3) except that a ringing current andexchange battery voltage detector 152 are not present. As illustrated inFIG. 5, cellular terminal 120 includes transceiver 250 or other meansfor communicating with wide area cellular network 100 when cellularterminal 120 is not within the local region 114 of base station 110 andfor communicating with transceiver 164 of base station 110 when cellularterminal 120 is within local region 114. Transceiver 250 is connected toantenna 122. Cellular terminal 120 further includes its own controlprocessor 254 and storage means 255 similar to those described withrespect to base station 110 and transmit circuit 251 and receive circuit253 for receive and transmit signal processing respectively.

As further shown in FIG. 5, when terminal 120 is a cellular phone, itincludes a keypad 257, a display 259, a speaker 261, and a microphone263. In order to provide a computer communications terminal for receiptand transmission of audio, video and data and/or multimedia signals,keypad 257 may be a full scale personal computer keyboard and display259 may be a large graphics display. A scanner 265 may also be providedas may other devices 267 such as disk drives and modems. The design ofterminal 120 is well known to those having skill in the art and need notbe described further herein.

As described above, radio communications between base station 110 andcellular terminal 120 occurs at a frequency assigned by the wide areacellular network provider to avoid same channel interference betweenbase station 110 and network cell station 102. As described above, thechannel selection means which obtains the channel within the cellularspectrum of wide area cellular network 100 for communications betweencellular terminal 120 and base station 110 is included in base station110. For non-multiplexed systems, any given frequency is one channel;however, for multiplexed type systems each frequency may carry multiplecommunications channels. The present description refers to frequency,however, it is to be understood that in a multiplexed system basestation 110 may be assigned a specific channel or slot using suchselected frequency.

The selected frequency may be entered into base station 110 fromexternal to base station 110 as an extracted digital control message, asdescribed above, in which case the frequency indicating signal isreceived by base station 110 by wire line communications over connector136. The frequency indicating signal is converted to a synthesizercommand and applied to line 217 to produce the requisite transmit andreceive frequency. The power level indicating signal is converted to atransmit power control signal and applied to line 220 to control thetransmit power. The conversions are preferably performed by controlprocessor 154 using conventional techniques. Operations performed to setthe frequency, and optionally power level, will be described below inconnection with FIG. 6.

The frequency indicating signal from the operator of wide area network100 is selected to minimize interference between base station 110 andnetwork cell station 102. Preferably, a frequency is utilized which isone of the frequencies within the cellular spectrum which is notallocated to the network cell station 102 in the cell 104 in which basestation 110 is located. More preferably, a frequency is selected fromthe group of frequencies within the cellular spectrum which is allocatedto a cell of wide area cellular network 100 which is farthest from saidbase station as illustrated in FIGS. 7 and 8.

The circuitry of base station 110 as illustrated in FIG. 3 furtherfunctions as a requesting means within housing 130, electricallyconnected to wire telephone line connector 136, for communicating withthe operator of wide area network 100 over wire network 108 using apredetermined service number stored in storage circuit 155. Controlprocessor 154 initiates a call using the predetermined service number bysending control and a data signals representing a request. Modem 166 andconverter 160 are used to transmit the request over line 136 as a knowntype of carrier which may be detected by a modem (not shown) set up forthis purpose by the operator of wide area cellular network 100. Theoperator of wide area cellular network assigns a frequency manually orautomatically, to reduce or avoid frequency interference. The requestedfrequency indicating signal from the operator of wide area cellularnetwork 100 is then received by modem 166 and an extracted digitalcontrol message is provided to control processor 154 as described above.An indication of the selected frequency is stored in storage circuit155, based upon the received frequency indicating signal. Alternatively,frequencies can be assigned via a removable frequency indicator, such asa "smart card" as described in copending application Ser. No. 08/093,076to Rydbeck entitled Method and Apparatus for Controlling TransceiverOperations in a Radio Communication System, assigned to the assignee ofthe present application, the disclosure of which is hereby incorporatedherein by reference.

A frequency indicating signal is also provided to cellular terminal 120when terminal 120 is parked in base station 110 and stored in storagemeans 255 as an indication of the selected frequency so that bothcellular terminal 120 and base station 110 have the selected frequencyinformation. Alternatively, the frequency information may be provided tocellular terminal 120 using the wide area cellular network 100 ifcellular terminal 120 is not parked in base station 110 and the userdoes not wish to park the terminal before initiating communicationsbetween base station 110 and cellular terminal 120 following a change inthe selected frequency.

The process of requesting a frequency indicating signal may be initiatedby the operator as an input using keyboard 144, for example, by pressing#0 to initiate calling the predetermined service number. Alternatively,the request may be initiated by control processor 154 responsive to alost connection signal from detector 152. The lost connection signal mayindicate that the connection of wire telephone line 136 to wiretelephone network 108 has been lost or that both the telephoneconnection and the power connection, based on the signal from powerdetection means 151 to control processor 154 have been lost, asdescribed above. Thus, the detector 152, power detection means 151 andcontrol processor 154 determine when a new frequency selection isrequired and initiate such a request.

Alternatively, the selected frequency information may be entered intobase station 110 using keyboard 144 which would likewise pass theinformation to control processor 154. This allows the user of basestation 110 to separately obtain the selected frequency information fromthe operator of wide area cellular network 100 and then manually inputthe data through keyboard 144.

The means for requesting and receiving the frequency indicating signalmay also be contained in cellular terminal 120. If this is the case,cellular terminal 120 may contact the operator of wide area cellularnetwork either through network cell station 102 or using telephone lineconnector 136 while cellular terminal 120 is parked in base station 110.Likewise, the input means for manually entering the request for afrequency indicating signal may be keypad 257 of cellular terminal 120.

If base station 110 is moved to a new location, any selected frequencypreviously used may be invalid and likely to cause interference withwide area cellular network 100 if transmissions from base station 110are allowed to occur without obtaining a new selected frequency from theoperator of wide area cellular network 100. It is desirable that basestation 110 include means responsive a detected loss of telephoneconnection or telephone and power connection loss as described above forpreventing transmission by transceiver 164 using the previously selectedfrequency. This may be readily accomplished by the circuitry illustratedin FIG. 3, as control processor 154 receives indicating signals fromboth detector circuit 152 and power detection means 151 which togetheract as a means for detecting loss of telephone and/or power connection.Control processor 154 may then control transceiver 164 to preventfurther transmissions. Control processor 154 may further send anindication to display 142 indicating that a new frequency needs to beobtained. Control processor 154 may also send a message to the operatorof the wide area cellular network via the PSTN network.

Initialization and channel acquisition operations according to U.S. Pat.No. 5,428,668 are illustrated in the flow chart of FIG. 6. Operationsare initialized at block 300 when base station 110 is obtained by theuser and plugged into a normal domestic telephone jack with telephoneconnector 136 and power outlet with power connector 134. On power up,detector 152 notifies control processor 154 that a telephone connectionhas been established to wire telephone line 108 and power sense signalfrom power detection means 151 notifies control processor 154 that linepower has been connected. At block 302 base station 110 calls the widearea cellular network using a predetermined service number. The servicenumber can be stored in base station 110, requiring only one or twokeypad depressions on keyboard 144 to effect dialling or may beinitiated automatically as described above. Alternatively, as describedabove, the user may contact the wide area cellular provider using adifferent phone and PSTN line and verbally request set-up informationwhich may then be manually keyed into base station 110. The servicenumber can appropriately be an "800" type number that is valid from alllocations.

After the call is initiated at block 302, base station 110 notifies thewide area cellular network operator of the location of base station 110at block 304. Using signalling facilities available in modern digitaltelephone networks, this may be accomplished by having the wide areacellular network operator request from the PSTN the number of the phoneline originating the call. At block 306 base station 110 requests acontrol message including a frequency, from the wide area cellularnetwork operator. The request may also include power level and channelinformation as well as frequency. At block 308 base station 110 receivesa control message including an indication of the requested frequencyfrom the wide area cellular network operator. This is then stored as anindication of the received frequency in base station 110 at block 310.

Base station 110 then transmits an indication of the received frequencyto cellular terminal 120 at block 312. This transmission may beaccomplished when cellular terminal 120 is parked in base station 110using system connector 132. Alternatively, a frequency indicating signalmay be transmitted by radio communications using transceiver 164 ifcellular terminal 120 is not parked in base station 110. Such atransmission may be made using the last frequency assigned to basestation 110 by the cellular network operator. Optionally, when it isnecessary to reallocate the base frequency when cellular phone 120 isnot parked in base station 110, the wide area network operator may placea call to cellular phone 120 over the cellular network and send a datamessage informing cellular terminal 120 of the change to the basefrequency. However, if the base frequency will not be frequentlyreallocated, base station 110 may notify the user of the need to parkcellular terminal 120 to obtain the new frequency information bydisplaying a warning message on display 142. At block 314 cellularterminal 120 stores an indication of the received frequency in cellularterminal 120.

Once the operating frequency for communications between base station 110and cellular terminal 120 has initially been established, the assignedfrequency will continue to be valid so long as base station 110 remainsin the same location. However, should base station 110 be moved to a newlocation, interference with the wide area cellular network could resultas the previously assigned frequency for base station 110 may be used inthe local cell of the wide area cellular network where base station 110is reinstalled. Consequently, at block 316 base station 110 determinesif the telephone connection to the base station has been lost since theindication of the requested frequency was last received as describedabove. Base station 110 may further determine if the power connection tobase station 110 has been lost since the indication of the requestedfrequency was last received. If the telephone connection or,alternatively, the telephone and power connections have been lost sincethe indication of the requested frequency was last received, basestation 110 repeats steps 300 through 314 as described above.Alternatively, at step 316 when it has been determined that theconnections have been lost base station 110 communications may bedisabled until a new request for a selected frequency is initiated.

The above operations were described for an embodiment using the basestation processor and keyboard to acquire the frequency information. Inan alternative embodiment the keyboard and processor of cellularterminal 120 may be used to carry out the initialization operations. Inthis embodiment, all of the steps of FIG. 6 would be carried out whilecellular terminal 120 was parked in base station 110. The communicationswith the wide area cellular network operator could then be handled bycellular terminal 120 with base station 110 serving to transmit signalsbetween cellular terminal 120 and the network operator over PSTN 108.

It is preferred that base stations 110 not be allocated frequencies thatare already in use in the cell of the wide area cellular network inwhich base station 110 is located, but to choose frequencies in use inthe cell which is a maximum distance away. Allocation of frequency bythe wide area cellular network provider in one embodiment is illustratedin FIG. 7. FIG. 7 illustrates a 21-cell frequency reuse pattern which isemployed in some United States wide area cellular networks to avoidinterference between neighboring cells. It is to be understood that awide area cellular network 100 may include a plurality of such reusepatterns, and thus include greater than the 21 cells illustrated in FIG.7. Each cell 104 in a cluster of 21 uses a different 1/21 fraction ofthe total number of frequencies available to the wide area cellularprovider. FIG. 7 shows the distribution of 21 groups of frequenciesnumbered 1 to 21 in a regularly spaced cell lattice. It may be seen thatthe cells using the same frequency groups are equispaced and root(21)cell diameters between centers where cell diameter is defined as thediameter of the inscribed circle of each hexagon.

It may be seen in FIG. 7 that cells numbered 15 or 8 are those mostdistant from the cells numbered 1. Therefore, the frequencies thatshould be used for base stations 110 located within cells numbered 1should be drawn from frequency groups 8 and 15. Reciprocally, thefrequencies used for base stations 110 located in cells numbered 15should be drawn from frequency groups 1 and 8 and so on for cellsnumbered 8. By symmetry, base stations 110 in cells numbered 2 shoulduse frequencies drawn from groups 9 and 16 and so forth. Thus, basestations 110 within each region may employ 2/21 of the total number offrequencies available. If this contains at least 21 frequencies, then a21-cell re-use plan can be employed to ensure that cells using the samefrequency are at least root(21) cell diameters apart. This requires thatthe total number of frequencies employed in both the cell and cellsystems is at least 21×21/2=220. This condition is normally satisfied inthe U.S. AMPS system, where two competing operators share over 800channels, having more than 400 each. Thus it is desirable that the cellsshould be capable of being programmed and reprogrammed to optimumfrequencies from the mobile telephone network according to the cell inwhich they are located.

FIG. 8 illustrates how base frequency allocations may be made in thecase of a cell re-use pattern such as the tighter, 7-cell pattern suchas may be employed in the European GSM system. As shown in FIG. 8,within each cell, different areas are allocated different sets offrequencies for use by base stations 110 located within thosesubregions. In FIG. 8, the frequency allocation patterns for basestations 110 are illustrated for the cells numbered 1 and 5respectively.

FIG. 9 illustrates a method for operation of the radio personalcommunications system once the frequency information has been acquiredby base station 110 and its associated cellular terminal 120. Operationsbegin when power is applied to cellular terminal 120 at Block 352. Uponapplication of power, cellular terminal 120 scans the selected frequencyallocated to its associated base station 110 at Block 354, anddetermines if a signal level above threshold has been detected, at Block356. If a signal level above threshold has been detected, then terminal120 is within the range 114 of its associated base station 110. Cellularterminal 120 then communicates at Block 360 over PSTN 108 by wirelesscommunications to base station 110. If a signal level above thresholdwas not detected, then the terminal 120 is not within the range 114 ofbase station 110 and communications are initiated with network cellstation 102 at Block 358, using conventional techniques.

It will be understood by those having skill in the art that a separatevoice channel frequency and power level may be used for transmissions bybase station 110 and terminal 120. The power levels may be different forthe base station and the terminal if, for example, the base station hasa larger antenna or a more sensitive receiver. It is also contemplatedthat the frequencies will be different since the terminal and basestation would not typically transmit or receive on the same frequenciesin a duplex transceiver. Alternatively, a single frequency and powerlevel may be obtained from the wide area cellular provider and a secondfrequency and power level may be determined from the single frequencyand power level.

Accordingly, the network provider/operator may allocate frequencies andpower levels of base station-to-terminal communications. By allocatingthe frequency and power level of base station-to-terminalcommunications, same frequency interference within a network cell isreduced and the network provider obtains additional revenue from thelicensed frequency spectrum for the base station.

Channel Allocation Using Received Signal Strength Measurements

Allocation of a cellular communications channel for communicationbetween a cellular terminal and a telephone base station using receivedsignal strength measurements according to the present invention will nowbe described. In general, during initialization of the telephone basestation, the cellular terminal is controlled to obtain downlinkmeasurements of received signal strength on all the control channels ofthe cellular system. The measurements are then relayed to the telephonebase station which transmits the measurements over the wire telephonenetwork line to a special service number connected to the wide areacellular network's central database. From these measurements, the widearea cellular network can derive the control channel with the lowestsignal strength. This control channel is associated with a wide areacellular network cell which is a large distance from the telephone basestation or a cell which is shadowed (blocked by obstructions). In eithercase, the wide area cellular network identifies the set ofcommunications channels (also known as "voice channels" or "trafficchannels") used by this cell and assigns this group of communicationschannels to the telephone base station. The set of control channels andcommunications channels used by a wide area cellular network arecollectively referred to as a wide area cellular network's "radiochannels".

The cellular terminal is then caused to perform a second frequency scan,to measure the received signal strengths on the frequencies in the setof communications channels which were just assigned. This scan willreveal the presence of other telephone base stations which use one ofthe frequencies in the set. The frequency with the lowest signalstrength is selected for use in communications between the cellularterminal and the telephone base station. This frequency is preferablyused by the telephone base station since it is far away or shadowed froma cell using this frequency and is far away or shadowed from anothertelephone base station using this frequency. Accordingly, the presentinvention creates an effective reuse pattern between telephone basestations within a given cell which is equal to the number of frequenciesin the set of communications channels.

If the signal level on the selected frequency is too high to beacceptable, then apparently all channels are used by nearby telephonebase stations and the reuse pattern may be unacceptable. The telephonebase station can then request from the wide area cellular network asecond group of channels, now corresponding to the measured cellularcontrol channel with the next lowest signal strength. This will increasethe effective reuse among the telephone base stations by a factor oftwo, thereby further reducing co-channel interference. By ordering thecellular terminal to obtain the downlink measurements and report them tothe telephone base station and the wide area cellular network, there isno need for a downlink receiver in the telephone base station itself.

Referring now to FIGS. 10A-10B, operations for channel allocation usingreceived signal strength according to the present invention will now bedescribed in detail. It will be understood that these operations arepreferably implemented by the control processor 154 of telephone basestation 110, the control processor 254 of cellular terminal 120 and thecontrol processor(s) of the wide area cellular network, operating understored program control. However, it will also be understood that specialpurpose hardware and/or combinations of special purpose hardware andgeneral purpose hardware operating under stored program control may beused.

As shown at Block 400, the cellular terminal is controlled to measureall of the control channels in the wide area cellular network. Theoperation of Block 400 may be initiated by telephone base station 110upon application of power thereto and/or upon connection to the wiretelephone network 108 as already described. The operation of Block 400may also be initiated by the wide area cellular network via the wiretelephone network connection to base station 110. In yet anotheralternative, this operation may be initiated by the cellular telephone,for example by user activation.

Preferably, after purchasing a telephone base station 110 and pluggingthe base station into a power source and a telephone jack, aninitialization procedure is started by the user, for example, by dialinga service number on the wire telephone network which links the telephonebase station to a central computer (control processor) including adatabase in the wide area cellular network. The wide area cellularnetwork checks the validity of the telephone base station using anauthentication procedure. The user may then be instructed to park thecellular telephone in the telephone base station so that a physicalconnection (electrical, electromagnetic such as optic, or acoustic)between the cellular telephone and the telephone base station is made.Alternatively, the wide area network operator can use the cellulartelephone interface between the cellular network and the cellularterminal to transmit the instructions.

The wide area cellular network operator instructs the cellular telephoneto scan all of the control channels of the wide area cellular network.In this scan, the cellular telephone identifies only the controlchannels in the wide area cellular network. As is known to those havingskill in the art, each cell includes one or more control channels whichgenerally use a constant, fixed transmit power and which carries acontinuous data stream of control information. These control channelshave formats such as fixed frequency, fixed frequency/time slot orspecial identifiers in the data stream, so that the cellular telephonecan recognize these channels as being control channels. From each ofthese control channels, the cellular telephone makes a signal strengthmeasurement.

As shown in Block 402, the cellular terminal transfers the controlchannel measurements to the telephone base station via the physicalconnection shown at 132 in FIG. 2. As shown at Block 404, the telephonebase station transfers the control channel measurements to the wide areacellular network via the wire telephone network (136 in FIG. 2).Alternatively, the cellular telephone can directly send the measurementinformation to the wide area cellular network through the nearest cell102.

Referring to Block 406, the wide area cellular network identifies thechannel with the lowest received signal strength. Because of the fixedfrequency reuse plan at a wide area cellular network, the wide areacellular network can also identify a first set of communicationschannels which are associated with the control channel having lowestsignal strength. Because of the fixed channel reuse pattern, all cellsusing this control channel will use the same group of communicationschannels so that no particular cell needs to be identified. All of thechannels in this group are potential candidates for the telephone basestation to use, since they are transmitted by a cell which is weaklyreceived in the telephone base station location due a large separationor shadowing.

It will also be understood by those having skill in the art that thecellular terminal itself may identify the control channel having thelowest received signal strength and transmit this control channel to thewide area cellular network. In yet another alternative, the telephonebase station may identify the control channel with the lowest receivedsignal strength and transfer this control channel to the wide areacellular network. However, in order to reduce the complexity of thecellular telephone and base station, the identification of the lowestreceived signal strength is preferably performed by the wide areacellular network, upon receipt of the relayed signal strengthmeasurements from the base station.

Still referring to FIGS. 10A-10B, the wide area cellular networktransfers identification of the communication channel set associatedwith the control channel having lowest signal strength to the telephonebase station via the wire telephone network. At Block 412, the telephonebase station transfers identification of the communication channel setto the cellular terminal. It will also be understood that the operationsof Blocks 408 and 412 may be accomplished via wireless communicationbetween the wide area cellular network and the cellular terminal.

At Block 414, the cellular terminal is caused to measure all thechannels in the identified communication channel set. At Block 416, thecellular terminal transfers the communication channel measurements tothe telephone base station. At Block 418, the telephone base stationtransfers communication channel measurements to the wide area cellularnetwork via the wire telephone network. It will also be understood thatthe operations of Blocks 416 and 418 may be accomplished by directlytransmitting the communication channel measurements to the wide areacellular network from the cellular terminal. At Block 422, the wide areacellular network selects the communications channel having the lowestsignal strength. As described above in connection with Block 406, thisselection may also take place in the cellular terminal or in thetelephone base station.

It will be understood that the received signal strength of the lowestcommunications channel may be too high so that freedom from co-channelinterference cannot be assured with acceptable certainty. See Block 424.If this is the case, then at Block 426, the wide area cellular networkidentifies a next set of communications channels associated with thecontrol channel having the next lowest signal strength. Operations ofBlocks 408-422 are then performed on the next set of communicationschannels. These operations may be performed repeatedly until at Block424 an acceptable communications channel having acceptably low signalstrength is identified. Then, at Block 428, the wide area cellularnetwork transfers identification of the selected communications channelto the telephone base station via the wire telephone network. At Block432, the telephone base station transfers the identification of theselected communications channel to the cellular terminal. Finally, atBlock 434, the cellular terminal and telephone base station communicatein the local area using the selected communications channel.

A numerical example of the operations of FIGS. 10A-10B in a wide areacellular network 100 of FIG. 7 having a 21-cell channel reuse patternwill now be described. A 21-cell frequency re-use pattern is employed insome United States wide area cellular networks to avoid interferencebetween neighboring cells. A 21-cell cluster uses control channels F₋₋1a, F₋₋ 2a, . . . F₋₋ 21a which are all unique in the cluster. Each cellis assigned one control channel. Associated with each control channelF₋₋ ia where i=1, . . . 21, is a group of communications channels. Thenumber of communications channels depends on the total number offrequencies licensed by the wide area network operator. Thecommunications channels may be designated F₋₋ ib, F₋₋ ic, F₋₋ id, . . .where i=1, . . . 21. At Block 400 of FIG. 10, the telephone base stationin cell 1 measures the signal strengths of control channels F₋₋ 1a, F₋₋2a, . . . F₋₋ 21a. See FIG. 7. Since control channels F₋₋ 15a and F₋₋ 8aare transmitted by the most distant cells, their received signalstrengths will most likely be the weakest. However, if a building islocated between the telephone base station location and cell 4, F₋₋ 4amight be very weak and a candidate for use.

The signal strength measurement reports of control channels F₋₋ 1a . . .F₋₋ 21 are reported to the wide area cellular network (Blocks 402 and404) which identifies the weakest control channel, say F₋₋ 15a. At Block406, the wide area cellular network identifies the set of communicationschannels used in cell 15 and associated with control channel F₋₋ 15a;i.e. the set of F₋₋ 15b, F₋₋ 15c, F₋₋ 15d, . . . . This identificationis transferred to the telephone base station (Block 408) and to thecellular terminal (Block 412). The control channel F₋₋ 15a itself is notincluded, as explained below.

The cellular terminal is then caused to make signal strengthmeasurements on the channel group just assigned: F₋₋ 15b, F₋₋ 15c, F₋₋15d, . . . . See Block 414. This measurement is not performed to measurethe traffic activity in cell 15, but rather to sense the presence ofnearby telephone base stations that already have been allocated one ofthe channels in the group. Again the reports are transferred to thetelephone base station (Block 416), which now can either select thechannel with the weakest signal strength itself, or retransmit thereports to the wide area cellular network (Block 418). The cellularnetwork selects the channel in the group F₋₋ 15b, F₋₋ 15c, F₋₋ 15d . . .with the lowest signal strength, at Block 422.

The channel selected from the group is used as the telephone basestation channel. This channel minimizes both the mutual interferencebetween the telephone base station and the cellular environment becauseit is selected from the best cellular reuse group, and the mutualinterference among the telephone base stations themselves because theweakest channel in the group was selected.

By selecting the best channel from the group, the telephone base stationenvironment provides an automatic channel allocation with an effectivereuse which equals the number of channels in the set. If there are notenough channels in the set to provide sufficient co-channel interferencesuppression, the telephone base station will recognize this in thesecond frequency scan, since the weakest channel in the group will stillhave a signal strength above that required. See Block 424. Then thetelephone base station can request the wide area cellular network toassign a second group of channels (Block 426), which corresponds to thenext weakest control channel.

In the above example, if F₋₋ 15a was the weakest channel, but F₋₋ 8a wasthe next weakest, then the wide area cellular network operator willassign a second group F₋₋ 8b, F₋₋ 8c, F₋₋ 8d . . . to the telephone basestation at Block 426. Again the cellular terminal will scan the signalstrengths on all the channels of this second group (Block 414) and theweakest is selected (Block 422). By having two groups available, theeffective reuse between the telephone base stations is doubled. Theseoperations can be repeated if required in order to solve co-channelinterference problems in hot spots where many closely-spaced telephonebase stations are located.

The cellular control channel itself is not included in the groupassignment for many reasons. First, if a telephone base station selectsa cellular control channel as the telephone base station channel, thenanother telephone base station may mistakenly identify the signals fromthat nearby telephone base station as being a nearby cellular baseduring initialization. As a result, the initializing telephone basestation will not consider the associated communications channel group,although it is likely that there are attractive channels in this groupsince it was selected by a nearby telephone base station. Another reasonnot to include the control channel is to avoid interference between thecontrols of the telephone base station and cellular systems. Finally,cellular communications channels are more likely to give lowinterference than cellular control channels. Control channels have totransmit continuously at a constant, high power level. Communicationschannels are used intermittently (only when they are used for a voice ordata communication), have DTX, and can apply automatic power control toreduce interference.

While the invention has been described primarily in terms of allocatedfrequencies, it is to be understood that the present invention islikewise directed to systems utilizing any form of multiplexing whereina single frequency carries a plurality of channels. In such a system,the present invention obtains from the external source such as the widearea cellular network operator both assigned frequency information andthe specific channel slot within the assigned frequency. Accordingly,the term "channel" as used herein includes frequency plus channel orfrequency alone. It is also to be understood that the present inventionmay be used within any cellular type wireless communications systemwhich incorporates any type of channel reuse pattern over a wide areacommunications network.

It will also be understood that the telephone base station need not useone particular communications channel from the set of assignedcommunications channels. Rather, all the communications channels fromthe assigned set may be used by employing sequential hopping. Thehopping set is the set of communications channels used by a cell whichis far away from the telephone base station. In this embodiment, signalstrength measurements on the allocated communications channels need notbe performed in order to minimize co-channel interference from nearbytelephone base stations. Rather, this interference is minimized due tothe nature of the sequential hopping, since each base station usesnon-synchronized hopping with different hopping sequences. The cellularterminal can be readily adapted to use sequential hopping whencommunicating with the telephone base station since sequential hoppingcan be applied in the wide area cellular network as well, for example inthe GSM system.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

That which is claimed:
 1. A method for allocating a cellularcommunications channel for communication between a cellular terminal anda telephone base station, the telephone base station connecting a wiretelephone network to the cellular terminal within a local region in acell of a wide area cellular network which uses a plurality of controlchannels and communications channels within a cellular network spectrum,said allocating method comprising the steps of:controlling said cellularterminal to measure received signal strengths of the control channels;identifying a set of communications channels associated with a measuredcontrol channel having lowest received signal strength; causing saidcellular terminal to measure received signal strengths of the set ofcommunications channels; selecting from said set of communicationschannels, a communications channel having lowest received signalstrength; and using the selected communications channel having lowestreceived signal strength for communication between said cellularterminal and said telephone base station within the local region.
 2. Amethod according to claim 1 wherein said selecting step is preceded bythe steps of:determining whether the received signal strength of thecommunications channel having lowest received signal strength issufficiently low; and repeating said identifying step and said causingstep on a next set of communications channels associated with a measuredcontrol channel having next lowest received signal strength, if thereceived signal strength of the channel having lowest received signalstrength is not sufficiently low.
 3. A method according to claim 1wherein said identifying step comprises the steps of:transferring thecontrol channel received signal strength measurements from said cellularterminal to said telephone base station; transferring the controlchannel received signal strength measurements from the telephone basestation to the wide area cellular network via said wire telephonenetwork; causing said wide area cellular network to identify a measuredcontrol channel having lowest received signal strength; and causing thewide area cellular network to identify the set of communicationschannels associated with the measured control channel having lowestreceived signal strength.
 4. A method according to claim 3 wherein saidstep of causing said cellular terminal to measure received signalstrengths of the set of communications channels is preceded by the stepsof:transferring the identified set of communications channels to saidbase station from said wide area cellular network via said wiretelephone network; and transferring the identified set of communicationschannels from said base station to said cellular terminal.
 5. A methodaccording to claim 4 wherein said selecting step comprises the stepsof:transferring the communication channel received signal strengthmeasurements from said cellular terminal to said telephone base station;transferring the communication channel received signal strengthmeasurements from the telephone base station to the wide area cellularnetwork via said wire telephone network; causing said wide area cellularnetwork to identify a measured communications channel having lowestreceived signal strength; and causing the wide area cellular network toselect from the set of communications channels, a communications channelhaving lowest received signal strength.
 6. A method according to claim 5wherein said using step is preceded by the steps of:transferringidentification of the selected communications channel to said basestation from said wide area cellular network via said wire telephonenetwork; and transferring the identification of the selectedcommunications channel from said base station to said cellular terminal.7. A method according to claim 1 wherein said controlling step, saididentifying step, said causing step and said selecting step are allpracticed while said cellular terminal is parked in said telephone basestation.
 8. A method according to claim 1 wherein said controlling step,said identifying step, said causing step and said selecting step are allpracticed while said cellular terminal is parked in said telephone basestation, via transfer of electrical signals, electromagnetic signals oracoustic signals between the telephone base station and the cellularterminal which is parked therein.
 9. A measuring method for a cellularterminal and a telephone base station, the telephone base stationconnecting a wire telephone network to the cellular terminal within alocal region in a cell of a wide area cellular network which uses aplurality of radio channels within a cellular network spectrum whereinsaid cellular terminal communicates with said telephone base stationusing one of said radio channels within said cellular network spectrum,said measuring method comprising the steps of:controlling said cellularterminal to measure received signal strengths of selected radiochannels; transferring the received signal strength measurements fromsaid cellular terminal to said telephone base station; and transferringthe received signal strength measurements from the telephone basestation to the wide area cellular network via said wire telephonenetwork.
 10. A method according to claim 9 further comprising the stepof:comparing the received signal strength measurements in the wide areacellular network to thereby identify a radio channel having low receivedsignal strength.
 11. A method according to claim 9 wherein saidcontrolling step is preceded by the steps of:transferring identificationof the selected radio channels to said base station from said wide areacellular network via said wire telephone network; and transferring theidentification of the selected radio channels from said base station tosaid cellular terminal.
 12. A system for allocating a cellularcommunications channel for communication between a cellular terminal anda telephone base station, the telephone base station connecting a wiretelephone network to the cellular terminal within a local region in acell of a wide area cellular network which uses a plurality of controlchannels and communications channels within a cellular network spectrum,said allocating system comprising:means for controlling said cellularterminal to measure received signal strengths of the control channels;means, responsive to said controlling means, for identifying a set ofcommunications channels associated with a measured control channelhaving lowest received signal strength; means, responsive to saididentifying means, for causing said cellular terminal to measurereceived signal strengths of the set of communications channels; andmeans, responsive to said causing means, for selecting from said set ofcommunications channels, a communications channel having lowest receivedsignal strength, such that the selected communications channel havinglowest received signal strength is used for communication between saidcellular terminal and said telephone base station within the localregion.
 13. A system according to claim 12 wherein said selecting meanscomprises:means for determining whether the received signal strength ofthe communications channel having lowest received signal strength issufficiently low; and means, responsive to said determining means, forusing the selected communications channel having lowest received signalstrength for communication between said cellular terminal and saidtelephone base station within the local region, if the received signalstrength of the channel having lowest received signal strength issufficiently low.
 14. A system according to claim 12 wherein saididentifying means comprises:means for transferring the control channelreceived signal strength measurements from said cellular terminal tosaid telephone base station; means for transferring the control channelreceived signal strength measurements from the telephone base station tothe wide area cellular network via said wire telephone network; meansfor causing said wide area cellular network to identify a measuredcontrol channel having lowest received signal strength; and means forcausing the wide area cellular network to identify the set ofcommunications channels associated with the measured control channelhaving lowest received signal strength.
 15. A system according to claim14 wherein said means for causing said cellular terminal to measurereceived signal strengths of the set of communications channels furthercomprises:means for transferring the identified set of communicationschannels to said base station from said wide area cellular network viasaid wire telephone network; and means for transferring the identifiedset of communications channels from said base station to said cellularterminal.
 16. A system according to claim 15 wherein said selectingmeans comprises:means for transferring the communication channelreceived signal strength measurements from said cellular terminal tosaid telephone base station; means for transferring the communicationchannel received signal strength measurements from the telephone basestation to the wide area cellular network via said wire telephonenetwork; means for causing said wide area cellular network to identify ameasured communication channel having lowest received signal strength;and means for causing the wide area cellular network to select from theset of communications channels, a communications channel having lowestreceived signal strength.
 17. A system according to claim 16 whereinsaid selecting means further comprises:means for transferringidentification of the selected communications channel to said basestation from said wide area cellular network via said wire telephonenetwork; and means for transferring the identification of the selectedcommunications channel from said base station to said cellular terminal.18. A measuring system for a cellular terminal and a telephone basestation, the telephone base station connecting a wire telephone networkto the cellular terminal within a local region in a cell of a wide areacellular network which uses a plurality of radio channels within acellular network spectrum, said measuring system comprising:means forcontrolling said cellular terminal to measure received signal strengthsof selected radio channels; first means, responsive to said controllingmeans, for transferring the received signal strength measurements fromsaid cellular terminal to said telephone base station; and second means,responsive to said first means, for transferring the received signalstrength measurements from the telephone base station to the wide areacellular network via said wire telephone network.
 19. A system accordingto claim 18 wherein said wide area cellular network furthercomprises:means for comparing the received signal strength measurementsto thereby identify a communications channel having low received signalstrength.
 20. A system according to claim 18 wherein said controllingmeans further comprises:means for transferring identification of theselected radio channels to said base station from said wide areacellular network via said wire telephone network; and means fortransferring the identification of the selected radio channels from saidbase station to said cellular terminal.
 21. A radio personalcommunications system comprising:a wide area cellular network includinga plurality of cells which use a plurality of control channels andcommunications channels within a cellular network spectrum; a cellularterminal; a telephone base station, the telephone base stationconnecting a wire telephone network to the cellular terminal within alocal region of a cell; said cellular terminal comprising means formeasuring received signal strengths of the control channels; said widearea cellular network including means for identifying a set ofcommunications channels associated with a measured control channelhaving low received signal strength, for using at least one of thecommunications channels for communication between said cellular terminaland said telephone base station within the local region.
 22. A systemaccording to claim 21 wherein said wide area cellular network furthercomprises means for directing said cellular terminal to measure receivedsignal strengths of the set of communications channels;said cellularterminal further comprising means, responsive to said identifying means,for selecting from said set of communications channels, a communicationschannel having low received signal strength, and for using the selectedcommunications channel having lowest received signal strength forcommunication between said cellular terminal and said telephone basestation within the local region.
 23. A system according to claim 22wherein said wide area cellular network further comprises:means fordetermining whether the received signal strength of the communicationschannel having lowest received signal strength is sufficiently low; andmeans for directing said cellular terminal to measure received signalstrengths of a next set of communications channels associated with ameasured control channel having next lowest received signal strength, ifthe received signal strength of the channel having lowest receivedsignal strength is not sufficiently low.
 24. A system according to claim21 wherein said base station comprises:means for receiving the controlchannels received signal strength measurements from said cellularterminal; and means for transferring the control channel received signalstrength measurements from the telephone base station to the wide areacellular network via said wire telephone network.
 25. A system accordingto claim 24 wherein said base station further comprises:means forreceiving the identified set of communications channels from said widearea cellular network via said wire telephone network; and means fortransferring the identified set of communications channels from saidbase station to said cellular terminal.
 26. A system according to claim22 wherein said base station further comprises:means for receiving thecommunication channel received signal strength measurements from saidcellular terminal; and means for transferring the communication channelreceived signal strength measurements to the wide area cellular networkvia said wire telephone network.
 27. A system according to claim 26wherein said base station further comprises:means for receivingidentification of the selected communications channel from said widearea cellular network via said wire telephone network; and means fortransferring the identification of the selected communications channelto said cellular terminal.
 28. A system according to claim 21 whereinsaid base station further comprises means for mechanically coupling saidcellular terminal thereto; andmeans for transferring electrical signals,electromagnetic signals or acoustic signals between the telephone basestation and the cellular terminal which is mechanically coupled thereto.29. A measuring method for a cellular terminal and a telephone basestation, the telephone base station connecting a wire telephone networkto the cellular terminal within a local region in a cell of a wide areacellular network which uses a plurality of radio channels within acellular network spectrum, said measuring method comprising the stepsof:transferring signal strength measuring instructions from said widearea cellular network to said telephone base station via said wiretelephone network; transferring said signal strength measuringinstructions from said telephone base station to said cellular terminal;controlling said cellular terminal to measure received signal strengthsof selected radio channels in said local region according to said signalstrength measuring instructions; and identifying at least one radiochannel for communication between said telephone base station and saidcellular terminal in said local region, based upon the measured receivedsignal strengths of the selected radio channels in the local region. 30.A method according to claim 29 wherein the following step is performedafter said controlling step:transferring the measured received signalstrengths from said cellular terminal to said telephone base station.31. A method according to claim 30 wherein the following step isperformed after said step of transferring the measured received signalstrengths from said cellular terminal to said telephone basestation:transferring the measured received signal strengths from saidtelephone base station to said wide area cellular network via said wiretelephone network.
 32. A method according to claim 31 wherein saididentifying step is performed by said wide area cellular network.
 33. Amethod according to claim 32 wherein said identifying step is followedby the step of:transferring identification of the at least one radiochannel from said wide area cellular network to said telephone basestation via said wire telephone network.
 34. A method according to claim33 wherein said step of transferring identification of the at least oneradio channel from said wide area cellular network to said telephonebase station via said wire telephone network is followed by the step oftransferring said identification of the at least one radio channel fromsaid telephone base station to said cellular terminal.